A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs).
When a substrate undergoes different lithography steps and process steps, a surface of the substrate can be contaminated by contaminating particles. The contaminating particles can be clamped between the substrate and the substrate table. Due to the presence of the contaminating particle, the substrate will be locally deformed. This causes focus and overlay errors. A similar issue arises for other objects, such as a patterning device.
It is desirable to reduce overlay and focus errors caused by particle contamination of objects such as the substrate and the patterning device.